1. Field of the Invention
This invention pertains to expanded food products with high protein content and the method of making the same.
2. Discussion of the Related Art
It is problematic that current manufacturing practices are unable to accommodate certain food ingredients for use in making expanded food products which are suitable for certain needs. By way of example, such low carbohydrate diets as the popular Atkins diet and variations thereof have created a significant demand for food with high protein and reduced carbohydrates. It is a technological challenge to increase protein content in certain categories of traditional foods, particularly in expanded products such as breakfast cereals and crispy snacks. Expanded food products are traditionally made using extrusion technology and contain a significant amount of starch to accommodate proper expansion. The starch generally imparts desired organoleptic qualities in the final food product.
Starches have unique properties, for example, facilitating the formation of continuous films under extrusion conditions. The physico-chemical nature of starch benefits the expansion of food products by forming a good cell structure matrix with correspondingly favorable texture in the final expanded products. Extrusion becomes more difficult, however, when ingredients such as proteins, dietary fibers and lipids are added. It is difficult to expand proteins without denaturation in extrusion processing because protein materials are molecularly less amenable to expansion that derives from the high temperature and pressure of extrusion processing. In particular, wheat gluten protein has an elastic nature that resists expansion and texturizes easily.
Extrusion processing has long been used to manufacture expanded food products, but the problem of obtaining non-soy high protein content has not been resolved. In one example, U.S. Pat. No. 3,873,748 issued to Schwab et al. describes a method to make ready-to-eat flake cereal by cooking, extruding, drying and grinding a basic cereal matrix and then blending the resulting product with sodium caseinate, rewetting the mixture and extruding to form pellets, and finally using high pressure rolls to create the flakes. The resulting cereal contains up to 25 percent (25%) protein, which is rather low.
Some success has been obtained using soy proteins. U.S. Pat. No. 3,852,491 issued to Malzahan et al. describes the use of high temperature/high pressure (HTHP) extrusion to produce an expanded cereal containing up to fifty-five percent (55%) soy protein. Soy protein isolate having up to 80% protein was processed at temperatures in the range of 220° F. to 355° F. and at pressures in the range from 1000 to 3000 psig. A product having a stringy or protein fiber-like texture developed when the temperature of the extruded dough mass reached 355° F. or higher. Cereal-like textures were observed only at lower temperatures. This fiber-like texture that is obtained indicates the texturization process.
U.S. Pat. No. 3,965,268 issued to Stocker et al. describes an expanded soy food product that is obtained by extrusion with heating of a mixture containing an organic compound and water with passage from a high pressure zone to a low pressure zone. The product has an open cell structure and could be used as a meat substitute, convenience food or pet food ingredient. A sulfur-containing organic material provides functional expansion benefit when added to the mixture in an amount ranging from 0.2 to 0.6% by weight of the proteinacious material. The sulfur-containing organic material includes sulfur-containing amino acids, lower alkyl mercaptans, lower alkyl sulfides, lower alkyl disulfides, thioacids, or their salts.
U.S. Pat. No. 6,242,033 B1 issued to Sander et al. describes an extrusion process for making expanded high-protein cereal. Tuber starch, such as tapioca, is used as an expanding agent. The products contained protein levels of 50% to a maximum of 70%. Specific recipes were disclosed, largely using rice flour and tapioca flour and soy protein isolates with the protein levels between 50% and 62%.
If carefully observed all the methods deal with extrusion processing of recipes which have a significant amount of starch, which is a critical component in expansion of the product. Expansion of starches during extrusion also requires a proper balance of water content with other ingredients and proper extrusion conditions as are known generally in the art to obtain a good stable expansion. The unique molecular properties of starches aid in their expansion. They form continuous films when extruded, which helps to form very good complete cell structure when extruded.
Extrusion becomes difficult when other ingredients such as proteins and lipids are added into the recipes. Unmodified proteins, when extruded with starches, disperse into the matrix of starch. Then the product property may entirely depend on the extent of dispersion of the proteins into the starch matrix.
When regular unmodified proteins are used, it is difficult to extrude them, as it takes more energy to break the disulfide bonds and arrange them properly in a streamline. For example, when vital wheat gluten is used in large amounts in the production of bread dough or other products, the dough becomes too strong and is difficult to process during mixing, shearing, kneading and molding. In particular, the elasticity of wheat-based proteins tends to collapse such products after expansion.
Most of the high protein products that have been developed include soy as a main source of protein. During the extrusion process soy proteins are easier to work with, although if high levels of soy proteins are used, they adversely affect flavor and give unacceptable volume and crumb grain properties.
Wheat gluten is a binary mixture of gliadin and glutenin. These components can be separated by alcohol fractionation or by using a non-alcoholic process (as disclosed in U.S. Pat. No. 5,610,277) employing the use of organic acids. Gliadin is soluble in 60-70% alcohol and comprises monomeric proteins with molecular weights ranging from 30,000 to 50,000 Daltons. These proteins are classified as alpha-, beta-, gamma-, omega-gliadins depending on their mobility during electrophoresis at low pH. Gliadin is primarily responsible for the extensible properties of wheat gluten. Glutenin is the alcohol insoluble fraction and contributes primarily to the elastic or rubbery properties of wheat gluten. Glutenin is a polymeric protein stabilized with inter-chain disulfide bonds and made up of high-molecular weight and low molecular weight subunits. Generally, glutenin exhibits a molecular weight exceeding one million daltons. Preferred fractionated wheat protein products comprise at least about 85% by weight protein, and more preferably at least about 80% by weight of glutenin, all proteins expressed on N×6.25, dry basis.
Wheat protein isolates are generally derived from wheat gluten by taking advantage of gluten's solubility at alkaline or acidic pH values. Wheat gluten is soluble in aqueous solutions with an acidic or alkaline pH and exhibits a classical “U-shaped” solubility curve with a minimum solubility or isoelectric point at a pH 6.5-7.0. By dissolving the gluten, proteins can be separated from non-protein components by processes like filtration, centrifugation, or membrane processing followed by spray drying. Alternatively, wet gluten from wet processing of wheat flour can be repeatedly kneaded, water washed, and dewatered to get rid of contaminating starch and other non-protein components, and subsequently flash dried. These techniques yield a wheat protein isolate product with elevated protein content that is usually at least about 85% by weight, and more preferably at least about 90% by weight (on a N×6.25, dry basis). Wheat protein isolates are less elastic but more extensible than wheat gluten. Examples of preferred wheat protein isolates include, Arise™ 3000, Arise™ 5000, Arise™ 6000 and Arise™ 8000 available from MGP Ingredients, Inc., Atchison, Kans.
Wheat protein concentrates are proteinaceous compositions which preferably have protein contents of at least about 70% by weight, and preferably at least about 82% by weight (N×6.25 dry basis). Wheat protein concentrates may be of different varieties manufactured by a number of different methods. Vital wheat gluten is one type of wheat protein concentrate that has a protein content of at least about 82% by weight (N×6.25, dry basis). Vital wheat gluten is a viscoelastic protein manufactured by a flash drying method. Additional types of wheat protein concentrates are manufactured by dispersing wet gluten in an ammonia solution followed by spray drying. These wheat protein concentrates exhibit lesser viscoelastic properties than vital wheat gluten but tend to be more extensible. Examples of the latter type of wheat protein concentrates include FP 300, FP 600 and FP 800 available from MGP Ingredients, Inc. of Atchison, Kans.
Native starch has often been modified to satisfy specific needs for food manufacturers. Chemical modifications, such as hydroxypropylation, cross-linking, and oxidation are commonly used to enhance shear, temperature, and acidic processing stability, to improve freeze and thaw stability, and to increase paste clarity and stability. Starch undergoes structural changes during chemical modification in some of its glucopyranosyl units in the molecule.
Hydroxypropylated starch is formed by reaction with propylene oxide normally at very low levels of substitution. Substituted hydroxypropyl groups restrict interaction of starch chains and prevent junction zone formation. Without cross-linking, however, hydroypropylated starch tends to swell excessively during cooking and form a stringy paste that is unstable against high shear and acidic processing. Combination of hydroxylpropylation and cross-linking is an efficient method of modification to improve storage stability. This type of starch includes Midsol™ 46, available from MGP Ingredients.
Oxidation of starch by an oxidizing agent such as sodium hypochlorite is well known. During the oxidation reaction, hydroxyl groups on starch molecules are oxidized to carbonyl and carboxyl groups. Cleavage of some of the glycosidic linkages also occurs, which decreases molecular weight of starch. Oxidized starch granules tend to swell at lower temperature to a greater extent than unmodified starch. Other characteristics of oxidized starch include low and stable viscosity, forming gel of high clarity, and improved binding and film forming properties. Midsol™ Krisp, available from MGP ingredients, is categorized as this type of starch.
Some dietary starches resist digestion by α-amylase in the human upper gastrointestinal tract and are termed as resistant starch (RS). RS is recognized as a type of dietary fiber and is of particular interest with respect to its health benefits against colon cancer. A high level of RS in starchy food constitutes a diet with a low glycemic index, which is thought to be beneficial for all individuals, especially for type II diabetics. A certain degree of cross-linking on granular starch leads to the formation of resistant starch, for example, as reported in U.S. Pat. No. 5,855,946 issued to Seib et al., and limits the digestion by α-amylase. This type of starch is supplied by MGP Ingredients and is commercially available as FiberSym™ 70 and FiberSym™ 80-ST.
Functional characteristics of resistant starch may be modified by preswelling of granular starch before cross-linking, for example, as described in U.S. Pat. No. 6,299,907 issued to Seib et al. The preswollen and cross-linked starch granules are capable of undergoing multiple hot or cold water swelling cycles without losing the individuality of starch granules. Reversibly swellable starch products may be modified further by an oxidizing agent. Oxidized reversibly swellable starch products are characterized by improved hydrophilic surface properties without undue agglomeration or clumping. Oxidized reversibly swellable starch displays stability improvement with hydrophilic polymers such as hydrocolloids and proteins.